To improve our understanding of the causes of drug abuse, experiments are proposed to test the possibility that one drug can acquire the ability to elicit the \effects normally produced by a second drug as the result of classical conditioning procedures. More specifically, the studies investigate whether administration of a low dose of one drug can be made to elicit the sensory effects characteristic of withdrawal from a different drug (or craving for the second drug). A series of six experiments using rats is proposed. The first of these replicates a previously demonstrated conditioning effect using body temperature as the dependent variable. Subsequent experiments incrementally shift the focus of attention into the domain of sensory effects of drugs. The final experiment tests whether a low dose of ethanol can, after classical conditioning procedures, evoke the sensory effects normally produced by withdrawal form narcotics.